John Deere QAS 70 troubleshooting: 16 symptom-cause-remedy entries from the manufacturer's own service documentation.
John Deere QAS 70 — full specs, parts & maintenance.
| Symptom | Cause | Remedy |
|---|---|---|
| Alternator gives 0 Volt | Blown fuse | Replace fuse |
| Alternator gives 0 Volt | No residual voltage | Excite the alternator by applying a 12V battery voltage with a 30 W resistor in series on the + and - terminals of the electronic regulator, respecting the polarities |
| After being excited the alternator still gives 0 Volt | Connections are interrupted | Check connection cables, measure winding resistances and compare with values mentioned in the alternator manual |
| Low voltage at no load | Voltage potentiometer out of setting | Reset voltage |
| Low voltage at no load | Intervention of protection | Check frequency/voltage regulator |
| Low voltage at no load | Winding failure | Check windings |
| High voltage at no load | Voltage potentiometer out of setting | Reset voltage |
| High voltage at no load | Failed regulator | Substitute regulator |
| Lower than rated voltage at load | Voltage potentiometer out of setting | Reset voltage potentiometer |
| Lower than rated voltage at load | Intervention by protection | Current too high, power factor lower than 0.8; speed lower than 10% of rated speed |
| Lower than rated voltage at load | Failed regulator | Substitute regulator |
| Lower than rated voltage at load | Rotating bridge failure | Check diodes, disconnect cables |
| Higher than rated voltage at load | Voltage potentiometer out of setting | Reset voltage potentiometer |
| Higher than rated voltage at load | Failed regulator | Substitute regulator |
| Unstable voltage | Speed variation in engine | Check regularity of rotation |
| Unstable voltage | Regulator out of setting | Regulate stability of regulator by acting on STABILITY potentiometer |
Fault codes and symptom→remedy steps extracted from this model’s service/owner documentation; verify against the official manual before servicing.
Documented causes: Voltage potentiometer out of setting; Intervention by protection; Failed regulator; Rotating bridge failure. See the table for the matching fixes.
Documented causes: Voltage potentiometer out of setting; Intervention of protection; Winding failure. See the table for the matching fixes.
Documented causes: Blown fuse; No residual voltage. See the table for the matching fixes.